In prior art electrocatalytic gas diffusion electrodes or structures of electrochemical cells and the like, gas has been fed or applied by one of three modes. For example, a plenum can be filled with gas in contact with substantially all of one face of an electrocatalytic electronically conducting gas-porous substrate, such as carbon cloth, with the other face being in contact with the electrolyte of the cell (as, for example, in commonly owned U.S. Pat. No. 4,331,520. Alternatively, the gas can be mixed; with an electrolyte solution external to or in the cell and the "mixed phase" can be caused to flow over or through the faces of the electrocatalytic structure (as, for example, in commonly owned U.S. Pat. No. 4,422,911. More recently, the gas has been exposed only to the edge or rim portion of the electrocatalytic electrode in a chamber external to and isolated from the electrolyte, as in commonly owned U.S. Pat. No. 4,478,696.
In U.S. Pat. No. 4,248,682, gas diffusion/current collector electrode assemblies are described which involve electrocatalytic carbon cloths and a variety of gas-permeable metallic current-collecting means designed to allow gas access to the cloth through the current collector by the first of the three above-mentioned gas-accessing modes.